This invention relates to a method and apparatus for recording and reconstructing holograms using incoherent light.
It was recognized early on that holograms, which are normally implemented utilizing coherent light, can also be formed with incoherent or partially coherent light. In ordinary holography each object point, i.e., the intensity at lateral and longitudinal locations, is interferometrically recorded as a Fresnel Zone Plate (FZP) using photographic medium. In any system, including incoherent coded aperture imaging systems, in which each object point is coded as a FZP, the image can be reconstructed by optical diffraction and can be viewed as an hologram.
Several schemes have been proposed for incoherent recording, such as interferometric systems including an amplitude splitting interferometer, based on a double-focus birefringent lens. See G. Cochran, J. Opt. Soc. Am. 56 1513 (1966), H. R. Worthington, J. Opt. Soc. Am. 56 1397 (1966), G. W. Stroke and R. C. Restrick III, App. Phy. Lett. 7, 229 (1965), and A. W. Lohmann, J. Opt. Soc. Am 55, 1555 (1965).
All such incoherent holographic schemes are relatively cumbersome, or require complicated mechanical or electrical apparatus. The low signal-to-bias ratio that is inherent in incoherent holography, is also a severe limitation. See Collier, et al., "Optical holography," Chap. 20 Academic Press, (1971). The present invention permits the recording and reconstruction of holograms with incoherent light, utilizing the properties of optical propagation in birefringent crystals wherein two interfering light beams have identical geometrical paths.